When a dam project in Thailand turned a national park into a lake, scientists from UC San Diego began studying a dozen small mammal species on its newly minted islands, figuring they had 50 to 100 years before the animals disappeared.

Some of the creatures vanished in 15 years. Nearly all were gone within a quarter century, setting a record for local extinctions, and offering a global warning about the hazards of habitat fragmentation.

“It was like ecological Armageddon,” said Luke Gibson, a former UC San Diego graduate student now completing his doctorate at the National University of Singapore, who served as lead author of the study, published last week in the journal Science.

Researchers began studying populations of native rats, mice and tree shrews in 1990, after construction of a hydroelectric dam flooded a national park, leaving about 90 forested hilltops as isolated islands in a lake.

Initially the animals seemed unaffected by the change, but 25 years later nearly all disappeared.

“Our result, of everything gone in 25 years, was two to three times faster than expected,” said David Woodruff, said David Woodruff, a professor of biology at UC San Diego who instigated the study.

The loss of species was due to the area effect, in which fragmented parcels lack resources to support animals, and to invasions by non-native rats, Woodruff said.

The findings offer parallels to San Diego County and other areas with similarly splintered habitat. Where patches of coastal sage and chaparral in areas such as Mission Valley and North County are separated by housing and other development, Woodruff said the same effects apply. And here domestic cats step in to hunt lizards, rodents and birds in the fragmented parcels, he said.

“We’re left with bits of vegetation, but all the essential animals are gone,” he said. “That’s a wake-up call to biologists that if we’re trying to save wildlife for its own value or for the ecological services it provides us, we don’t have as much time as we thought.”